Method for producing fiber-reinforced plastic molding, preform and method for producing same, and adhesive film

ABSTRACT

The present invention is a method for producing a fiber-reinforced plastic molding including, in the following order, the steps of: forming a preform laminate fixed to a molding die by laminating a plurality of preforms each including a dry fiber fabric and a fixing resin, the preforms being laminated through the fixing resin formed on a surface of the dry fiber fabric and including a partially-cured thermosetting resin exhibiting tackiness at a room temperature; impregnating the dry fiber fabric, provided in the preform laminate fixed to the molding die, with a liquid thermosetting resin; curing the liquid thermosetting resin and the fixing resin to form a fiber-reinforced plastic molding; and demolding the fiber-reinforced plastic molding from the molding die.

TECHNICAL FIELD

The present invention relates to a method for producing afiber-reinforced plastic molding under a pressure-reduced atmosphere, apreform used in the method, a method for producing the preform, and anadhesive film used for producing the preform.

BACKGROUND ART

Fiber-reinforced plastic (FRP) attracts attention in various industrialfields as light-weighted and high-strength material. In recent years, toproduce a relatively large fiber-reinforced plastic molding at a lowcost, there has been employed a vacuum assist resin transfer molding(VaRTM) for molding fiber-reinforced plastic under a pressure-reducedatmosphere by means of vacuum absorption. The vacuum assist resintransfer molding is a method for obtaining a fiber-reinforced plasticmolding including the steps of covering a dry fiber fabric arranged in amolding die with a bag film, vacuum-absorbing the bag film, infusing aliquid resin into the bag film, impregnating the fiber fabric withresin, and curing the resin (for example, refer to PTL1: Japanese PatentLaying-Open No. 60-83826).

However, since a dry fiber fabric has no tackiness (viscosity), the dryfiber fabric itself cannot be fixed at a position against gravity in thestep of forming into a three-dimensional shape (the step of arranging adry fiber fabric on a molding die, the step of laminating a dry fiberfabric on a dry fiber fabric, and the like). Further, when a dry fiberfabric and a molding die, or a dry fiber fabric and a dry fiber fabricare not in sufficient contact with each other, fibers in some casesexhibited wrinkles under the pressure-reduced condition.

As a simplified method for solving such a problem, a method isconceivable using a tape to fix a portion being subject to trimming andnot eventually used in a finished product. However, there is a problemthat a portion which can be fixed using a tape is limited, and that theoperation is cumbersome and results in low productivity.

Therefore, there have been proposed a method for fixing a dry fiberfabric with use of solution with a binder containing an amorphousthermoplastic resin (tackifier: spray) (for example, refer to PTL2:Japanese Patent Laying-Open No. 2004-269705) and a method for shorteningthe step of laminating dry fiber fabrics by adhering a plurality offiber fabrics each other in advance by means of an adhesive resincomposed of a mixture of a thermoplastic resin (toughness) andthermosetting resin (for example, refer to PTL3: Japanese PatentLaying-Open No. 2004-114586).

The method disclosed in PTL2 can be used in the step of arranging a dryfiber fabric on a molding die and in the step of laminating a dry fiberfabric on a dry fiber fabric, allowing the operation time to beshortened. However, when the method is used in the step of arranging adry fiber fabric on a molding die, a non-cured thermoplastic componentis exposed at the surface of a demolded fiber-reinforced plasticmolding. Therefore, there has been a problem that the surface which wasin contact with the molding die may become sticky and that athermoplastic component may exhibit white dots to cause poor appearance.

Further, the method disclosed in PTL 3 can be used in the step oflaminating a dry fiber fabric on a dry fiber fabric, allowing theoperation time to be shoretened. However, the method cannot be used inthe step of arranging a dry fiber fabric on a molding die. Further, whena plurality of fiber fabrics are combined in advance, and a large numberof layers are present, shaping with respect to a bent portion becomesdifficult. Particularly, the tension applied to the fiber will differbetween the inside and outside, resulting in occurrence of wrinkles dueto loosening of fibers.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent Laying-Open No. 60-83826-   PTL 2: Japanese Patent Laying-Open No. 2004-269705-   PTL 3: Japanese Patent Laying-Open No. 2004-114586

SUMMARY OF INVENTION Technical Problem

In light of the problems described above, an object of the presentinvention is to provide a preform which can prevent viscosity on asurface and poor appearance due to occurrence of white dots in afiber-reinforced plastic molding which can be obtained by a method forproducing a fiber-reinforced plastic molding under a pressure-reducedatmosphere, and which can be used in both of the step of fixing a dryfiber fabric on a molding die and the step of laminating dry fiberfabrics, a method for producing the preform, and an adhesive film usedfor producing the preform.

Solution to Problem

The present invention is directed to a method for producing afiber-reinforced plastic molding including, in the following order, thesteps of: forming a preform laminate fixed to a molding die bylaminating a plurality of preforms each including a dry fiber fabric anda fixing resin, the preforms being laminated through the fixing resinformed on a surface of the dry fiber fabric and including apartially-cured thermosetting resin exhibiting tackiness at a roomtemperature; impregnating the dry fiber fabric, provided in the preformlaminate fixed to the molding die, with a liquid thermosetting resin;curing the liquid thermosetting resin and the fixing resin to form afiber-reinforced plastic molding; and demolding the fiber-reinforcedplastic molding from the molding die.

In the step of forming the laminate, the plurality of preforms arelaminated taking in consideration of fiber orientation of the dry fiberfabric to fabricate a preform laminate, and thereafter the preformlaminate can be fixed to the molding die.

In the step of forming a laminate, after fixing the preform to themolding die through the fixing resin, at least one preform may befurther laminated through the fixing resin.

The fixing resin is a vinyl ester resin having both of a (meta-)acryloyl group and an epoxy group in an identical resin skeleton and isa partially-cured resin with the solely reacted epoxy group. The liquidthermosetting resin is a vinyl ester resin, and the fixing resin and theliquid thermosetting resin are preferably cured at the same time in thestep of curing.

In the step of curing, curing of the thermosetting resin is preferablyperformed by a stepcure, and complete curing of the fixing resin ispreferably performed during an aftercure of the liquid thermosettingresin. The dry fiber fabric is a carbon fiber, and the fixing resinpreferably includes carbon black.

Further, the present invention also relates to a preform used forproducing a fiber-reinforced plastic molding, and the preform includes adry fiber fabric and a fixing resin. The fixing resin is formed on asurface of the dry fiber fabric and includes a partially-curedthermosetting resin exhibiting tackiness at a room temperature. Thefixing resin is preferably formed in a regular dot pattern.

Further, the present invention also relates to a method for producingthe preform, including the step of transferring the fixing resin to thedry fiber fabric.

Preferably, in the step of transferring, an adhesive film including arelease paper or release film and a fixing resin, formed on a surface ofthe release paper or release film and including a partially-curedthermosetting resin exhibiting tackiness at a room temperature, isbrought into close contact with the dry fiber fabric to transfer thefixing resin to the dry fiber fabric.

Further, the present invention also relates to an adhesive filmincluding a release paper or release film and a fixing resin, formed ona surface of the release paper or release film and including apartially-cured thermosetting resin exhibiting tackiness at a roomtemperature.

Preferably, the adhesive film is used for the method for producing apreform. Preferably, the fixing resin is formed in a regular pattern soas to cover 0.05%-5% of an area of the release paper or release film.Preferably, the fixing resin is formed in a regular dot pattern.

Advantageous Effects to Invention

A fixing resin used in the present invention (a partially-curedthermosetting resin exhibiting tackiness at room temperature) does notcontain a large amount of thermoplastic component. Therefore, even whenthe fixing resin is used on a surface in contact with a molding die, noviscosity and white dot occur. Therefore, a fiber-reinforced plasticmolding exhibiting fine appearance can be obtained.

Further, a preform of the present invention includes the fixing resin.Therefore, a position of the preform can be fixed without being affectedby gravity, so that the step of shaping into a three-dimensional shape(the step of arranging a dry fiber fabric on a molding die, the step oflaminating a dry fiber fabric on a dry fiber fabric, and the like) canbe simplified, resulting in improved productivity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a cross-sectional view schematically presenting an example ofan adhesive film of the present invention.

FIG. 1B is a perspective view of FIG. 1A.

FIG. 1C is a perspective view presenting another example of an adhesivefilm of the present invention.

FIGS. 2( a)-2(c) are cross-sectional views schematically presenting anexample of the steps for producing a preform of the present invention.

FIG. 3 is a cross-sectional view schematically presenting a methodaccording to the present invention for shaping a preform into a moldingdie.

FIG. 4 is a cross-sectional view schematically presenting a condition ofthe step of impregnating in the method for producing a fiber-reinforcedplastic molding according to the present invention.

DESCRIPTION OF EMBODIMENTS

<Preform>

A preform of the present invention is a member including a dry fiberfabric and a fixing resin, and the fixing resin is formed on a surfaceof the dry fiber fabric and includes a partially-cured thermosettingresin exhibiting tackiness at a room temperature. The preform is usedfor producing a fiber-reinforced plastic molding. Herein, the surface ofthe dry fiber fabric does not include an inner surface within a space inthe fiber fabric.

Preferably, the fixing resin is formed so as not to interruptimpregnation of a dry fiber fabric with a liquid thermosetting resin aswill described later. For example, the fixing resin is preferably formedin a dot pattern or in a spider web pattern, and more preferably formedin the dot pattern. Accordingly, impregnation of the liquidthermosetting resin is not interrupted even in the area to which thefixing resin is transferred.

<Method for Producing Preform>

Next, a method for producing a preform will be described. FIG. 2 showsan example of the steps for producing a preform of the presentinvention. Firstly, from the state shown in FIG. 2( a), a fixing resin 2of an adhesive film 3 is brought into contact with one side surface of adry fiber fabric 4. Then, a release film 1 is peeled off to obtain apreform 5 a shown in FIG. 2( b) with fixing resin 2 attached to the oneside surface of dry fiber fabric 4.

As described above, the method for producing a preform according to thepresent invention preferably includes the transferring step oftransferring a fixing resin to a dry fiber fabric. Further, in the stepof transferring, an adhesive film including a release paper or releasefilm and a fixing resin (a partially-cured thermosetting resinexhibiting tackiness at a room temperature) formed on a surface of therelease paper or release film are preferably brought into close contactwith a dry fiber fabric to transfer the fixing resin to the dry fiberfabric.

Further, as shown in FIG. 2( c), another preform 5 a fabricated in asimilar manner may be laminated on preform 5 a through fixing resin 2,so that a preform laminate 5 b composed of a plurality of laminatedpreforms 5 a can be obtained. As described above, fabricating a preformlaminate in advance eliminates the necessity to shape all of preforms 5a one by one on a molding die.

Dry fiber fabric 4 may be a fabric of a carbon fiber, a glass fiber, aZyron fiber, a Kevlar fiber, and the like. Preferably, a fabric of acarbon fiber and a glass fiber may be used.

<Adhesive Film>

Next, an adhesive film used in the method for producing a preform willbe described. An adhesive film of the present invention includes arelease paper or release film, and a fixing resin (a partially-curedthermosetting resin exhibiting tackiness at a room temperature) formedon a surface thereof the release paper or release film.

An example of the adhesive film of the present invention is shown inFIG. 1A and FIG. 1B. FIG. 1A is a schematic cross-sectional view, andFIG. 1B is a perspective view. As shown in FIGS. 1A and 1B, adhesivefilm 3 includes release film 1 and fixing resin 2 (a partially-curedthermosetting resin exhibiting a tackiness at the room temperature)formed on release film 1 in a regular dot pattern.

The fixing resin may be, for example, an epoxy resin, a polyimide resin,and a phenol resin, but is not particularly limited as long as thefixing resin is a partially-cured thermosetting resin exhibitingtackiness at a room temperature. Preferably, the fixing resin is a vinylester resin having both of an (meta-) acryloyl group and an epoxy groupin an identical resin skeleton. The fixing resin may contain pigmentsuch as carbon black. The fixing resin may contain a small amount oftackifier such as rosin ester. Further, a release paper or the like maybe used in place of the release film.

Another example of the adhesive film of the present invention is shownin FIG. 1C. In place of the adhesive film with a fixing resin formed ina regular dot pattern shown in FIGS. 1A and 1B, an adhesive film with afixing resin formed in a regular spider web pattern shown in FIG. 1C maybe employed.

Preferably, the fixing resin is formed in a regular pattern so as tocover 0.05% -5% of an area of the release paper or release film. This isbecause the fixing resin may fall down following gravity in the case ofbeing less than 0.05% and may inhibit impregnation of resin in the caseof being greater than 5%.

Using the adhesive film according to the present invention allowsproduction of a preform merely by transferring a fixing resin to a dryfiber fabric, so that a needed amount of fixing resin can be suitablyused at a needed part.

<Method for Producing a Fiber-Reinforced Plastic>

Next, a method for producing fiber-reinforced plastic will be described.A method for producing fiber-reinforced plastic according to the presentinvention includes, in the following order, the steps of: forming apreform laminate fixed to a molding die by laminating a plurality ofpreforms each including a dry fiber fabric and a fixing resin, thepreforms being laminated through the fixing resin formed on a surface ofthe dry fiber fabric and including a partially-cured thermosetting resinexhibiting tackiness at a room temperature; impregnating the dry fiberfabric, provided in the preform laminate fixed to the molding die, witha liquid thermosetting resin; curing the liquid thermosetting resin andthe fixing resin to form a fiber-reinforced plastic molding; anddemolding the fiber-reinforced plastic molding from the molding die.

A first embodiment of the step of forming a laminate may include themethod of laminating a plurality of preforms taking in consideration offiber orientation of a dry fiber fabric to fabricate a preform laminate,and thereafter fixing the preform laminate to a molding die. Accordingto this method, the preform laminate is formed in advance. Therefore,all of preforms are not required to be shaped one by one on the moldingdie, so that the operation of laminating the fibers can be shortened.However, since wrinkles may occur at a bent portion when fixed to themolding die, limiting the thickness of such portion or partiallyavoiding formation of the fixing resin are preferable to preventoccurrence of wrinkles at the time of fixing (shaping) the preformlaminate to the molding die.

A second embodiment of the step of forming a laminate may include themethod of attaching preforms to a molding die one by one to eventuallyobtain a preform laminate fixed to the molding die, in other words, themethod of fixing a preform to a molding die through a fixing resin andfurther laminating at least one preform through a fixing resin.According to this method, a preform laminate having an appropriate shapein conformity with a shape of the molding die can be shaped (formed andfixed).

A specific example of the first embodiment of the step of forming alaminate may include, for example, the method of shaping and fixing apreform laminate fabricated in advance to a molding die, covering thepreform laminate fixed to the molding die with a bag film and the like,vacuum-absorbing the bag, and impregnating the dry fiber fabric in thepreform laminate with a liquid thermosetting resin.

With reference to FIGS. 3 and 4, an example of a method for producing afiber-reinforced plastic molding using the first embodiment of the stepof forming a laminate will be described. Firstly, as shown in FIG. 3, amolding die 6 is prepared having a surface processed with a Teflon(registered trademark) coating 7, and preform laminate 5 b is broughtinto contact with molding die 6 through fixing resin 2 and fixed.Accordingly, fixing resin 2 fixes dry fiber fabric 4 to Teflon(registered trademark) coating 7 on the surface of molding die 6.Therefore, no positional displacement due to gravity occurs.

Next, as shown in FIG. 4, a peel ply 8 and a flow media 9 are arrangedon preform laminate 5 b, and the entirety is covered with a bagging film10 and sealed. At this stage, Teflon (registered trademark) tubes 101 a,101 b are provided at two locations on the edges of the sealed space andstopped with valves. Further, Teflon (registered trademark) tube 101 ais connected to a vacuum pump, and Teflon (registered trademark) tube101 b is connected to a resin tank.

Next, the vacuum pump is actuated to reduce pressure in the space sealedby bagging film 10. After the pressure is reduced in the sealed space, avalve of Teflon (registered trademark) tube 101 b on the side of theresin tank is opened, so that a liquid thermosetting resin 11 isabsorbed into the sealed space of a reduced pressure. Liquidthermosetting resin 11 impregnates into dry fiber fabric 4 whileexpanding though a large-mesh flow media 9. When liquid thermosettingresin 11 reaches Teflon (registered trademark) tube 101 a on the side ofthe vacuum pump, the valve of the Teflon (registered trademark) tube 101b on the resin supplying side is closed.

Then, liquid thermosetting resin 11 is left until gelated. Thereafter,the vacuum pump is disconnected, and annealing is performed using anoven or the like, so that liquid thermosetting resin 11 and fixing resin2 are completely cured together. Finally, separation at an interfacebetween peel ply 8 and fiber-reinforced plastic and at an interfacebetween molding die 6 and fiber-reinforced plastic is performed, so thatthe fiber-reinforced plastic can be obtained.

Liquid thermosetting resin 11 is not particularly limited as long as itis a low-viscosity thermosetting resin such as an epoxy resin, apolyester resin, a vinyl ester resin, and a cyanate ester resin.However, liquid thermosetting resin 11 is preferably a vinyl esterresin.

The condition for curing the fixing resin is preferably not differentfrom the condition for curing the liquid thermosetting resin. In thecase where the fixing resin is a vinyl ester resin having both of a(meta-) acryloyl group and an epoxy group in an identical resin skeletonand is a partially-cured resin with the solely reacted epoxy group, andthe liquid thermosetting resin is a vinyl ester resin, the fixing resinand the liquid thermosetting resin can be cured at the same time in thestep of curing. Therefore, the steps for production can be abbreviated,resulting in advantageous improvement of the production efficiency.

The step of curing is preferably performed by the stepcure of conductingthe steps of curing in a stepwise manner. The stepcure is composed of apre-step process (precure) and a post-step process (aftercure,postcure). The precure is a pre-process step in curing a thermosettingresin, and curing is performed to an extent of not obtaining a finalstrength, and a main object is to form a stable shape. Generally,preliminary curing is performed at a temperature slightly below theglass-transition point. The aftercure is a curing step for obtaining thefinal strength and is generally performed in an environment with ahigher temperature and a longer time than the precure. Performing thestep of curing by the stepcure can suppress to the minimum an influenceto the viscosity interface with different expansion coefficients due tothermal expansion and contraction.

During the aftercure for the liquid thermosetting resin, complete curingof the fixing resin is performed preferably. This is for preventingdeterioration of strength due to uncured state of resin.

Hereinafter, the present invention will be described more in detail withexamples. However, the present invention is not limited to theseexamples.

EXAMPLES Example 1

Firstly, mixed solution was prepared which contains: 100 parts by weightof a vinyl ester resin (M-7000 manufactured by Showa Highpolymer Co.,Ltd) having both of a (meta-) acryloyl group and an epoxy group in aresin skeleton; 3 parts by weight of an epoxy curing agent (Light EsterDM manufactured by Showa Highpolymer Co., Ltd.); and 1 part by weight oforganic peroxide (328E manufactured by Showa Highpolymer Co., Ltd.).

Next, an SUS plate (thickness 0.5 mm) having a plurality of holes with adiameter of 300 μm was superimposed on PET film 1 processed to bereleasable and having a thickness of 38 μm. Further on the SUS plate,the mixed solution was dropped, and printing with squeegee wasperformed, and then the SUS plate was released, so that the mixedsolution was scattered on PET film 1. Consequently, adhesive film 3having fixing resin 2 formed in a dot pattern as shown in FIGS. 1A and1B was obtained. Thereafter, drying was performed at 50° C. for an hour.In such a manner, while the epoxy group of the vinyl ester resin reactedwith the epoxy curing agent to increase its viscosity, and the (meta-)acryloyl group remained unreacted due to absence of a catalyst such ascobalt salt, thus a moderate tackiness (viscosity) was developed.

Next, as shown in FIG. 2, adhesive film 3 was superimposed on carbonfiber fabric 4 (T300 carbon fiber plain-woven cloth manufactured byToray Industries, Inc.) to transfer fixing resin 2 to carbon fiberfabric 4, so that preform 5 a was obtained. Next, preform 5 a wassuperimposed on preform 5 a, so that preform laminate 5 b was obtained.

Next, an L-shaped member of molding die 6 (made of aluminum and having athickness of 3 mm) having Teflon (registered trademark) coating 7 formedthereon was prepared. Next, as shown in FIG. 3, preform laminate 5 b wasarranged at a portion perpendicular to the ground. Here, preformlaminate 5 b adhered with fixing resin 2 and did not fall down bygravity.

Next, as shown in FIG. 4, peel ply 8 (BLEEDER LEASE-B manufactured byAirTech) and flow media 9 (GREEN FROW 75 manufactured by AirTech) werearranged on preform laminate 5 b, and the entirety was covered withbagging film 10 (WL7400 manufactured by AirTech) and sealed with asealing member (AT-200Y manufactured by AirTech). At this stage, tubes(outer diameter: 9.52 mm, and inner diameter: 6.35 mm) made of Teflon(registered trademark) (registered trademark, polytetrafluoroethylene)were provided at two locations on the edges of the sealed space andstopped with valves. One end was connected to a vacuum pump, and theother end was connected to a resin tank. Next, the vacuum pump wasactuated to reduce pressure in the sealed space.

Next, as shown in FIG. 4, peel ply 8 (BLEEDER LEASE-B manufactured byAirTech) and flow media 9 (GREEN FLOW 75 manufactured by AirTech) werearranged on preform laminate 5 b, and the entirety was covered withbagging film 10 (WL7400 manufactured by AirTech) and sealed with asealing member (AT-200Y manufactured by AirTech). At this stage, tubes(outer diameter: 9.52 mm, and inner diameter: 6.35 mm) made of Teflon(registered trademark) (registered trademark, polytetrafluoroethylene)were provided at two locations on the edges of the sealed space andstopped with valves. One end was connected to a vacuum pump, and theother end was connected to a resin tank. Next, the vacuum pump wasactuated to reduce pressure in the sealed space.

Example 2

Other than use of an epoxy resin as liquid thermosetting resin 11,fiber-reinforced plastic was produced in a manner similar to that ofExample 1. Other than the above, the fiber-reinforced plastic wasobtained according to the steps and conditions similar to those ofExample 1.

It should be understood that the embodiments and examples disclosedherein are illustrative and non-restrictive in every respect. The scopeof the present invention is defined by the terms of claims, rather thanthe description set forth above, and is intended to include anymodifications within the scope and meaning equivalent to the terms ofclaims.

Reference Signs List

1 release film; 2 fixing resin; 3 adhesive film; 4 dry fiber fabric; 5 apreform; 5 b preform laminate; 6 molding die; 7 Teflon (registeredtrademark) coating; 8 peel ply; 9 flow media; 10 bagging film; 11 liquidthermosetting resin; 101 a, 101 b Teflon (registered trademark) tube.

The invention claimed is:
 1. A method for producing a fiber-reinforcedplastic molding, comprising, in cited order, the following: mixing vinylester resin having both of a (meta-) acryloyl group and an epoxy groupin a resin skeleton, an epoxy curing agent, and organic peroxide toprepare a partially-cured vinyl ester resin with said epoxy groupreacted solely; forming a preform laminate by laminating a plurality ofpreforms each including a dry fiber fabric and a fixing resin, thepreforms being laminated through said fixing resin, said fixing resinbeing formed in a dot pattern on a surface of the dry fiber fabric andbeing said partially-cured vinyl ester resin; fixing the formed preformlaminate to a molding die via the fixing resin of one of the preforms;impregnating said dry fiber fabric, provided in said preform laminatefixed to said molding die, with a liquid vinyl ester resin; curing saidliquid vinyl ester resin and said fixing resin at the same time to forma fiber-reinforced plastic molding; and demolding said fiber-reinforcedplastic molding from said molding die.
 2. The method for producing afiber-reinforced plastic molding according to claim 1, wherein in saidcuring, curing of said liquid vinyl ester resin is performed during astepcure, and complete curing of said fixing resin is performed duringan aftercure of said liquid vinyl ester resin.